It is known in the art of broaching to provide for machines which utilize an endless chain for carrying a series of tools into contact with one or more workpieces. Typically, the endless chain is assembled from a plurality of articulated links, and the machine includes a housing for supporting the assembled endless chain and for defining a path of travel passing through a work zone where stock removal tools, carried by the articulated links, can engage the work as the endless chain is driven through the work zone. Examples of early machine designs of this type for producing spiral and helical gears are disclosed in U.S. Pat. Nos. 1,468,393; 1,469,602; 2,475,690; 2,692,537; and 2,749,804. Additionally my copending U.S. patent applications Ser. No. 930,252 and Ser. No. 930,779, both filed Aug. 2, 1978, disclose improvements in endless chain assemblies for machines of this type.
Machines utilizing an endless chain for carrying tools offer a potential for very high speed production of whatever shape of workpiece is being formed by the tools. In fact, in the case of gear production, it is contemplated that stacks of gear blanks may be worked simultaneously with machinery of this type, rather than one at a time as has been the case with many other types of gear forming machines. However, the requirements for gear manufacture are far more severe than those for other forms of broaching, and therefore, machines of the endless chain type have not been, as far as I know, commercially acceptable for high production gear manufacturing needs up to this time. The forming of gear tooth profiles on a work blank requires precise control of an engagement between a workpiece and each cutting tool making contact with the workpiece. This requirement demands, in turn, a very rigid machine which maintains precise placement of both workpiece and tool under a working load and for a sustained operation of the machine. Since an endless chain is by its very nature not as rigid as other forms of tool-holding equipment, it has been a problem in this art to design and manufacture an endless chain type of machine having the capability of high production manufacture of precision gears.
In my copending U.S. patent applications (identified above), I describe an improved type of endless chain apparatus in which the endless chain is firmly supported and carefully guided in its advancement through the critical work zone portion of its path of travel. This was partially accomplished by providing a supporting surface in the bed of the chain housing for firmly supporting the endless chain as its links were driven through the work zone area. In addition, gib means were carried adjacent the work zone for overlapping and pressing the endless chain into firm contact with the supporting surface, and this was done through a contact of the gib means with a pair of rollers carried by each link of the endless chain. As the endless chain entered the work zone portion of its travel, the rollers associated with the link were pressed toward the supporting surface of the chain housing by their rolling contact with the overlapping gib means carried along each edge of the work zone. This action, in turn, pressed the entire link toward the supporting surface in the bed of the chain housing. As each link advanced out of the work zone, its rollers became disengaged from the gib means and shifted their contact to guide surfaces provided throughout the remainder of the path of travel of the endless chain. This shifting from the gib means to the separate guide surfaces required a reversal of rotation of the pair of rollers associated with each link. Although such reversal in rotation is acceptable for many uses of this type of machine, there is a potential problem of unwanted wear taking place between the rollers and the guide surfaces which they contact in their course of travel from the work zone through the remainder of the chain housing.
In order to overcome any problems that may be associated with the guiding rollers of an endless chain, the present invention provides for two separate sets of rollers carried by the links of the endless chain for separately contacting the gib means (in the work zone) and the guiding surfaces (out of the work zone). The first set of rollers is carried in positions for contacting only the gib means as the endless chain is pressed into firm contact with the supporting surface of the chain housing in the work zone area of the machine. These rollers normally rotate only in the direction required for rolling contact with the gib means for advancement through the work zone. The second set of rollers is carried in positions which are out of contact with the gib means but which make rolling contact with the guide surfaces of the machine for all of the path of travel of the chain outside of the work zone area. The second set of rollers rotates only in a direction required for rolling engagement with the guide surfaces. Thus, the two sets of rollers can rotate in opposite directions at different times in the course of travel of the chain throughout its entire path of travel, and there is no requirement for a reversal of rotation of either set of rollers in whatever contact is being made with either the gib means or the guide surfaces of the machine. This provides for better control and support of the endless chain throughout its travel and eliminates the potential for unwanted wear of moving components which might otherwise be required to change direction of rotation very rapidly during the course of travel of the endless chain.
In accordance with a specific embodiment of the invention, each link making up the endless chain assembly is provided with a first pair of rollers mounted on opposite sides of the link for making rolling contact only with gib means associated with the apparatus. In addition, a second pair of rollers is mounted on opposite sides of the link for making rolling contact only with the guide surfaces associated with the apparatus. The first and second pairs of rollers are mounted on a common axis provided by separate shafts carried on opposite sides of the link for supporting the rollers. Each separate shaft supports one roller of the first pair and one roller of the second pair in a side-by-side relationship.
In order to further improve the rolling contact between the guiding rollers of the endless chain and the structures with which they make contact, there is optionally provided a means for initiating the rotation of the second set of rollers as the rollers leave the work zone area of the machine and before they make a full load bearing contact with the guide surfaces provided in the remainder of the machine. The means for initiating rotation comprises strips of relatively soft or resilient material which make initial contact with the rollers for the purpose of imparting a rotational moment thereto without engaging the rollers in a full load-bearing contact with the harder material of the guide surfaces which they ultimately contact. The softer material may comprise a strip of plastic or soft metal, and the strip may be of a configuration which provides for a diminishing contact between the roller and the strip as the roller advances toward a full contact with an associated guide surface.
These and other features and advantages of the present invention will become apparent in the more detailed discussion which follows, and in that discussion reference will be made to the accompanying drawings as briefly described below.